The present invention relates to treatments useful in subterranean operations, and more particularly, to methods of modifying the stress-activated reactivity of subterranean fracture faces and other surfaces in subterranean formations.
In the production of hydrocarbons from a subterranean formation, the subterranean formation should be sufficiently conductive to permit the flow of desirable fluids to a well bore penetrating the formation. One type of treatment used in the art to increase the conductivity of a subterranean formation is hydraulic fracturing. Hydraulic fracturing operations generally involve pumping a treatment fluid (e.g., a fracturing fluid or a “pad” fluid) into a well bore that penetrates a subterranean formation at a sufficient hydraulic pressure to create or enhance one or more pathways, or “fractures,” in the subterranean formation. The fluid used in the treatment may comprise particulates, often referred to as “proppant particulates,” that are deposited in the resultant fractures. The proppant particulates are thought to prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to a well bore.
One problem that may affect fluid conductivity in the formation after a fracturing treatment is the tendency for particulate material (e.g., formation fines, proppant particulates, etc.) to flow back through the conductive channels in the subterranean formation, which can, for example, clog the conductive channels and/or damage the interior of the formation or equipment placed in the formation. One well-known technique to prevent these problems is to treat the associated portions of a subterranean formation with a hardenable resin to hopefully consolidate any loose particulates therein to prevent their flow-back. Another technique used to prevent flow-back problems, commonly referred to as “gravel packing,” involves the placement of a gravel screen in the subterranean formation, which acts as a barrier that prevents particulates from flowing into the well bore.
Another heretofore unrecognized problem that can negatively impact conductivity is the tendency of mineral sediments in a formation to undergo chemical reactions caused, at least in part, by conditions created by mechanical stresses on those minerals (e.g., fracturing of mineral surfaces, compaction of mineral particulates). These reactions are herein referred to as “stress-activated reactions” or “stress-activated reactivity.” One type of these stress-activated reactions is diageneous reactions. As used herein, the terms “diageneous reactions,” “diageneous reactivity,” and “diagenesis” are defined to include chemical and physical processes that move a portion of a mineral sediment and/or convert the mineral sediment into some other mineral form in the presence of water. A mineral sediment that has been so moved or converted is herein referred to as a “diageneous product.” Any mineral sediment may be susceptible to these diageneous reactions, including silicate minerals (e.g., quartz, feldspars, clay minerals), carbonaceous minerals, metal oxide minerals, and the like.
Two of the principle mechanisms that diageneous reactions are thought to involve are pressure solution and precipitation processes. Where two water-wetted mineral surfaces are in contact with each other at a point under strain, the localized mineral solubility near that point increases, causing the minerals to dissolve. Minerals in solution may diffuse through the water film outside of the region where the mineral surfaces are in contact (e.g., in the pore spaces of a proppant pack), where they may precipitate out of solution. The dissolution and precipitation of minerals in the course of these reactions may reduce the conductivity of the formations by, among other things, clogging the conductive channels in the formation with mineral precipitate and/or collapsing those conductive channels by dissolving solid minerals in the surfaces of those channels.
Moreover, in the course of a fracturing treatment, new mineral surfaces may be created in the “walls” surrounding the open space of the fracture. These new walls created in the course of a fracturing treatment are herein referred to as “fracture faces.” Such fracture faces may exhibit different types and levels of reactivity, for example, stress-activated reactivity. In some instances, fracture faces may exhibit an increased tendency to undergo diageneous reactions. In other instances, fracture faces also may exhibit an increased tendency to react with substances in formation fluids and/or treatment fluids that are in contact with those fracture faces, such as water, polymers (e.g., polysaccharides, biopolymers, etc.), and other substances commonly found in these fluids, whose molecules may become anchored to the fracture face. This reactivity may further decrease the conductivity of the formation through, inter alia, increased diageneous reactions and/or the obstruction of conductive fractures in the formation by any molecules that have become anchored to the fracture faces.